Light source unit, optical scan apparatus, and image formation apparatus

ABSTRACT

A light source unit is provided which includes a light source with a plurality of light emission portions two-dimensionally arranged; a substrate on which the light source is mounted; a first support portion supporting the substrate; a bias member biasing the substrate towards the first support portion; a coupling element coupling a light beam emitted from the light source; a second support portion supporting the coupling element; and a holding member holding a position of the substrate relative to the first support portion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from JapanesePatent Application No. 2007-226178, filed on Aug. 31, 2007, and No.2008-82308, filed on Mar. 27, 2008, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light source unit emitting a lightbeam, an optical scan apparatus scanning a scan surface with a pluralityof light beams and an image formation apparatus incorporating such anoptical scan apparatus.

2. Description of Related Art

In the prior art, an image formation apparatus forming images by Carlsonprocess is known. For example, such an image formation apparatus scansthe surface of a rotating photoconductive drum with a light beam to forman electrostatic latent image, visualizes the electrostatic latent imageas a toner image, and fuses the toner image on a sheet of paper as arecording medium to form an image. This type of the image formationapparatus has been popularly used in simple printmaking for an on-demandprint system. There has been increasing demand for high-density imagesand high-speed image outputs.

Japanese Laid-open Patent Application Publication No. 2003-211728, forexample, discloses an image formation apparatus which has a light sourcesuch as a vertical cavity surface emitting laser (VCSEL) array withplural light emission portions two-dimensionally, monolithicallyarranged and is capable of concurrently scanning a scan surface withplural light beams.

Such a vertical cavity surface emitting laser array used in the imageformation apparatus is composed of the light emission portions on a chipcontained in a package, which is made of a ceramic material or the like.For mounting the light emission portions on a circuit board bysoldering, the mounted light emission portions are not uniform inheight. With such non-uniformity in height, the surface of the packageis inclined relative to the surface of the circuit board. As a result,positional relations between the individual light emission portions andthe circuit board surface may not be the same.

In such a light source unit the positions of optical elements such as acoupling element (lens) are often determined on the basis of the circuitboard surface. In this case, there will be a problem that the positionaldifference between each light emission portion and the circuit boardsurface leads to a positional difference between the optical elementsand each light emission portion.

For prevention of such a problem, Japanese Laid-open Patent ApplicationPublication No. 2004-6592 discloses a method for positioning the packagesurface relative to the optical elements in a semiconductor laser unitby elastically bending the circuit board to bring the package intocontact with the surface of a support member by pressure.

However, such a method still has a problem that enforcedly bending thecircuit board causes solder of electric components mounted thereon to bepeeled off, which may adversely accelerate deterioration of the laserunit over time, for example.

SUMMARY OF THE INVENTION

In view of solving the above problems, an object of the presentinvention is to provide a light source unit in which a light source canbe precisely positioned relative to an optical system at three places,so as to stably form high quality images, as well as to provide anoptical scan apparatus incorporating such a light source unit and animage formation apparatus incorporating such an optical scan apparatus.

According to a first aspect of the present invention, a light sourceunit comprises a light source with a plurality of light emissionportions two-dimensionally arranged, a substrate on which the lightsource is mounted, a first support portion supporting the substrate, abias member biasing the substrate towards the first support portion, acoupling element coupling a light beam emitted from the light source, asecond support portion supporting the coupling element, and a holdingmember holding a position of the substrate relative to the first supportportion.

Preferably, the light source comprises a light emitting elementincluding a plurality of light emission portions and a packagecontaining the light emitting element. Further, in order to position thelight source relative to the first support portion, the bias memberbiases the substrate towards the first support portion to make thepackage in contact with the first support portion.

Preferably, the bias member comprises an anchor portion which latchesthe substrate to restrict movement thereof in a direction orthogonal toan optical axis of the light source.

Preferably, the holding member is attached to the first support portionand is movable in an optical axis direction of the coupling element.

Preferably, the holding member is attached to the first support portionand comprises an engaging portion which is engaged with the substrate.

Preferably, the holding member holds the substrate in a directionorthogonal to an optical axis of the coupling element.

Preferably, the engaging portion is formed in one of wedge and trapezoidshapes.

Preferably, the light source comprises a plurality of holding membersholding a position of the substrate relative to the first supportportion.

Preferably, the light source unit further comprises a connector mountedon the substrate and connected with a wiring from outside, in which theholding member holds neighborhood of a portion of the substrate on whichthe connector is mounted.

Preferably, the holding member is disposed on a line in parallel to adirection from which the connector is connected or disconnected with thewiring.

According to a second aspect of the present invention, an optical scanapparatus scanning a scan surface with a light beam comprises the lightsource unit according to the first aspect of the present invention, anoptical deflector deflecting a light beam emitted from the light sourceunit, and an optical imaging system focusing the light beam deflected bythe optical deflector on the scan surface.

Preferably, in the optical scan apparatus, the light source unit isrotatably supported around the optical axis of the coupling element.

According to the third aspect of the present invention, an imageformation apparatus which forms a toner image according to anelectrostatic latent image obtained by image information, and fuses thetoner image on a recording medium for image formation, comprises theabove optical scan apparatus, a photoconductive drum on which anelectronic latent image is formed by the optical scan apparatus, adevelop unit visualizing the electrostatic latent image formed on thephotoconductive drum, and a transfer unit fusing a toner imagevisualized by the develop unit on a recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an image formation apparatus 500 accordingto the first embodiment of the present invention;

FIG. 2 is a perspective view of an optical scan apparatus 100 accordingto the first embodiment of the present invention;

FIG. 3 is a side view of the optical scan apparatus 100;

FIG. 4 is a perspective view of a light source unit 70 according to thefirst embodiment of the present invention;

FIG. 5 is a first development view of the light source unit 70;

FIG. 6 is a second development view of the light source unit 70;

FIG. 7A is a perspective view of a light source 10, and FIG. 7B is aplain view of a light emitting element 10 a;

FIG. 8 is an x to y cross sectional view of the light source unit 70 indirections;

FIG. 9 shows how the light source unit 70 is mounted;

FIG. 10 is a perspective view of a light source unit 70′ according tothe second embodiment of the present invention;

FIG. 11A is a perspective view of a holding member 81, and FIG. 11B is apartial side view thereof;

FIG. 12A is a perspective view of a holding member 82, and FIG. 12B is apartial side view thereof;

FIG. 13 shows a first example of how a first support portion 74 and asubstrate 76 are joined;

FIG. 14 shows a second example of how the first support portion 74 andthe substrate 76 are joined;

FIG. 15 is a first x to y cross sectional view of a modified example, alight source unit 70″; and

FIG. 16 is a second x to y cross sectional view of the light source unit70″.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinafter, the first embodiment of the present invention will bedescribed in detail with reference to FIGS. 1 to 9. FIG. 1 shows animage formation apparatus 500 according to the present embodiment.

The image formation apparatus 500 is, for example, a tandem type colorprinter which prints multi-color images by superimposing andtransferring black, yellow, magenta, and cyan color toner images ontosheets of paper. The image formation apparatus 500 as shown in FIG. 1comprises an optical scan apparatus 100, four photoconductive drums 30Ato 30D, a transfer belt 40, a paper feed tray 60, a paper feed roller54, a first resist roller 56, a second resist roller 52, a fuse roller50, a paper discharge roller 58, a not-shown controller collectivelycontrolling the respective components, and a housing 501 in rectangularsolid shape accommodating the components.

A paper discharge tray 501 a on which printed sheets are discharged isformed on the top surface of the housing 501. The optical scan apparatus100 is disposed under the paper discharge tray 501 a.

The optical scan apparatus 100 scans the photoconductive drum 30A with alight beam for black image components modulated by image informationsupplied from a higher-level device (such as personal computer).Similarly, it scans the photoconductive drum 30B with a light beam forcyan image components, the photoconductive drum 30C with a light beamfor magenta image components, and the photoconductive drum 30D with alight beam for yellow image components. The structure of the opticalscan apparatus 100 will be described later.

The four photoconductive drums 30A to 30D are cylindrical members andhave photoconductive layers on their surfaces which become electricallyconductive when illuminated with a light beam. They are disposed withequal interval in an X-axis direction under the optical scan apparatus100 in FIG. 1.

The photoconductive drum 30A is disposed at end of a reverse X-axisdirection (left side in FIG. 1) inside the housing 15 so that itslongitudinal direction is to be the Y-axis direction. Thephotoconductive drum 30A is rotated by a not-shown rotation mechanismclockwise (as indicated by black arrows) in FIG. 1. Around thephotoconductive drum 30A disposed are an electric charger 32A at 12o'clock position (upper side), a toner cartridge 33A at 2 o'clockposition and a cleaning case 31A at 10 o'clock position.

The electric charger 32A is disposed with a predetermined clearance overthe surface of the photoconductive drum 30A with its longitudinaldirection as the Y-axis direction. It electrically charges the surfaceof the photoconductive drum 30A with a predetermined voltage.

The toner cartridge 33A includes a cartridge body containing a toner ofblack image components and a develop roller charged with a voltage ofreverse polarity of that of the photoconductive drum 30A, and the like.The toner cartridge 33A supplies the toner in the cartridge body to thesurface of the photoconductive drum 30A via the develop roller.

The cleaning case 31A is provided with a cleaning blade of a rectangularshape with its longitudinal direction as the Y-axis direction, and it isdisposed so that one end of the cleaning blade gets in contact with thesurface of the photoconductive drum 30A. The toner sticking on thesurface of the photoconductive drum 30A is removed by the cleaning bladealong with the rotation of the photoconductive drum 30A and collected inthe cleaning case 31A.

The photoconductive drums 30B, 30C, 30D with the same structure as thatof the photoconductive drum 30A are placed in sequence on the right sideof the photoconductive drum 30A with a predetermined interval. They arerotated by a not-shown rotation mechanism clockwise (as indicated by theblack arrows) in FIG. 1. Similarly to the photoconductive drum 30A,electric chargers 32B, 32C, 32D, toner cartridges 33B, 33C, 33D,cleaning cases 31B, 31C, 31D are disposed around the photoconductivedrums 30B, 30C, 30D, respectively.

The electric chargers 32B, 32C, 32D with the same structure as that ofthe electric charger 32A are disposed to electrically charge thesurfaces of the photoconductive drums 30B, 30C, 30D with a predeterminedvoltage, respectively.

The toner cartridges 33B, 33C, 33D include cartridge bodies containingtoners of cyan, magenta, yellow image components and develop rollerscharged with a voltage of reverse polarity of that of thephotoconductive drums 30B, 30C, 30D, and the like, respectively. Thetoner cartridges 33B, 33C, 33D supply the toners in the cartridge bodiesto the surfaces of the photoconductive drums 30B, 30C, 30D via thedevelop rollers, respectively.

The structure and function of the cleaning cases 31B, 31C, 31D are thesame as those of the cleaning case 31A.

Hereinafter, a unit of the photoconductive drum 30A, the electriccharger 32A, the toner cartridge 33A, and the cleaning case 31A is to bereferred to as the first image formation station; likewise, a unit ofthe photoconductive drum 30B, the electric charger 32B, the tonercartridge 33B, and the cleaning case 31B as the second image formationstation, a unit of the photoconductive drum 30C, the electric charger32C, the toner cartridge 33C, and the cleaning case 31C as the thirdimage formation station, and a unit of the photoconductive drum 30D, theelectric charger 32D, the toner cartridge 33D, and the cleaning case 31Das the fourth image formation station.

The transfer belt 40 is a free end ring-like member and rolls overdriven rollers 40 a, 40 c placed under the photoconductive drums 30A,30D, respectively, and rolls over a drive roller 40B which is placed ata slightly lower position than the driven rollers 40 a, 40 c. The upperend surface of the transfer belt 40 is in contact with the lower endsurfaces of the photoconductive drums 30A, 30B, 30C, 30D. The transferbelt 40 is rotated counterclockwise (as indicated by the black arrows inFIG. 1) by counterclockwise rotation of the drive roller 40 b. Atransfer charger (transfer unit) 48 is applied with a voltage of areverse polarity of that of the electric chargers 32A, 32B, 32C, 32D andis placed close to one end of the transfer belt 40 in the X-axisdirection (right side in FIG. 1).

The paper feed tray 60 of a substantially rectangular solid shape isplaced under the transfer belt 40 and contains piled-up paper sheets 61for printing. The paper feed tray 60 has a feeder outlet of arectangular shape close to one end of the upper surface thereof in theX-axis direction (right side in FIG. 1).

The paper feed roller 54 extracts paper sheets 61 one by one from thepaper feed tray 60 to feed them to a gap formed between the transferbelt 40 and the transfer charger 48 via the first resist roller 56composed of a pair of rotary rollers.

The fuse roller 50 is composed of a pair of rotary rollers, and appliesheat and pressure to the paper sheets 61 to feed the paper sheets 61 tothe discharge roller 58 via the resist roller 52 composed of a pair ofrotary rollers. The discharge roller 58 is composed of a pair of rotaryrollers and discharges the paper sheets 61 to the discharge tray 501 a.

Next, with reference to FIGS. 2 and 3, the structure of the optical scanapparatus 100 will be described. FIG. 2 is a perspective view of theoptical scan apparatus 100 and FIG. 3 is a side view thereof.

The optical scan apparatus 100 comprises an optical imaging system andtwo optical incidence systems 200A, 200B. The optical imaging system iscomposed of a polygon mirror 104, an fθ lens 105, reflective mirrors106B, 106A disposed in sequence in the reverse X-axis direction of thepolygon mirror 104, a reflective mirror 108B disposed under the fθ lens105, a toroidal lens 107B disposed between the reflective mirrors 106Band 108B, a reflective mirror 108A disposed in the reverse X-axisdirection of the reflective mirror 106B, and a toroidal lens 107Adisposed between the reflective mirrors 106A and 108A, as well as an fθlens 305 and reflective mirrors 306C, 306D disposed in sequence in theX-axis direction of the polygon mirror 104, a reflective mirror 308Cdisposed under the fθ lens 305, a toroidal lens 307C disposed betweenthe reflective mirrors 306C and 308C, a reflective mirror 308D disposedin the X-axis direction of the reflective mirror 308C, and a toroidallens 307D disposed between the reflective mirrors 306D and 308D.

The optical incidence system 200A allows light beams for scanning thephotoconductive drums 30A, 30B to be incident on the polygon mirror 104,while the optical incidence system 200B allows light beams for scanningthe photoconductive drums 30C, 30D to be incident on the polygon mirror104.

The optical incidence systems 200A, 200B are optical systems to makelight beams to be incident on the deflection surface of the polygonmirror 104 from a direction which makes an angle of 120 or 60 degreesrelative to the X axis. As representatively shown in FIG. 2, the opticalincidence system 200B includes a light source unit 70, and an aperturemember 201, a beam splitter prism 202, a pair of liquid crystal elements203A, 203B, and a pair of cylindrical lenses 204A, 204B which aredisposed in sequence along the path for the light beam from the lightsource unit 70. For the sake of simplicity, xyz coordinate system isdefined here by rotating XY coordinates by 30 degrees around the Z axisin FIG. 2

FIG. 4 is a perspective view of the light source unit 70 which comprisesa substrate 76, a first support portion 74, a second support portion 72supporting a coupling element 11, and a holding member to maintain apositional relation between the substrate and the first support portion.

FIGS. 5, 6 are perspective development views of the light source unit70. As shown in the drawings, a longitudinal direction of the substrate76 is the x-axis direction, and it has a light source 10 and alight-receiving element 18 on a surface in the reverse y-axis direction,and a drive circuit driving the light source 10 and a monitor circuitmonitoring signals from the light receiving element 18 on the oppositesurface, for example. Also, three round holes 76 a and three slits 76 bare formed on the substrate 76 to surround the light source 10.

FIG. 7A is a perspective view of the light source 10 which is a verticalcavity surface emitting laser (VCSEL) array including a package 10 b ofa square plate and a light emitting element 10 a contained in thepackage 10 b.

The package 10 b is made of a ceramic material, for example, andincludes a frame with xy and zy cross sections in U-form and a glassplate in size equivalent to that of the frame and attached to a reversey-axis side surface thereof. It is filled with inert gas inside.

The light emitting element 10 a includes a light emission plane on whicha plurality of VCSELs (light emission portions) are two-dimensionallyarranged. As shown in FIG. 7B, 32 VCSELs are arranged in matrix in 4rows, 8 columns thereon (on the reverse y-axis side) to emit diffusionlight in the reserve y direction. The row direction is parallel to astraight line L1 which makes an angle θ1 with the x axis while thecolumn direction is parallel to the z axis. In the present embodiment,an interval Dz between the VCSELs in the sub scan direction is set to18.4 μm and that Dx in the main scan direction is set to 30 μm, forexample. Adjacent VCSELs in the z-axis (sub scan) direction are disposedwith an interval dz of 2.3 μm (=Dz/8). The light emitting element 10 ais contained in the package 10 b such that the light emission plane isparallel to the surface of the package 10 b on the reverse y side.

The light receiving element 18 in FIGS. 5, 6 is placed on the x-axisside of the light source 10 to output signals (photoelectric conversionsignals) according to intensity of incident light beams. It is used forintensity detection of light beams from the light source 10.

The first support portion 74 is a box-like member with an open surfaceon the reverse y-axis side and accommodates an optical guide system 20(FIG. 5). On a surface on the opposite side formed are rectangularconcavities 74 b, 74 c to be fitted with the light source 10 and thelight receiving element 18, as well as three cylindrical portions 74 aaround the concavity 74 b to insert through the three round holes 76 a,respectively. Also, a circular opening is formed on the bottom walls ofthe concavities 74 b, 74 c to be in communication with the first supportportion 74.

As shown in FIG. 6, the substrate 76 and the first support portion 74are joined with each other by fitting the light source 10 and lightreceiving element 18 into the concavities 74 b, 74 c and inserting thecylindrical portions 74 a through the round holes 76 a. The relativeposition therebetween is defined by mounting a substantially triangularbias member 78 on the cylindrical portions 74 a of the first supportportion 74.

The bias member 78 is formed by sheet metal processing on an elasticplate member and provided with three anchor portions 78 b and a bladespring 78 c, for example. The anchor portions 78 b are insertablethrough three slits 76 b on the substrate 76. The blade spring 78 c haselastic force acting in the reverse y-axis direction. The bias member 78is fixed on the first support portion 74 by screws 79. The screws 79 arescrewed into the cylindrical portions 74 a of the first support portion74 via the round holes 78 a formed at the corners of the bias member 78,respectively while the anchor portions 78 b are inserted into the slits76 b of the substrate 76. In such a manner, the blade spring 78 c of thebias member 78 biases the substrate 76 in a direction to approach thefirst support portion 74, and the reverse y-axis side surfaces of thelight source 10 and the light receiving element 18 are brought intocontact with the bottom walls of the concavities 74 b, 74 c of the firstsupport portion 74 by pressure, as shown in FIG. 8.

The holding member 77, as shown in FIG. 4, 5, is composed of aplate-like fixation portion fixed on the x-axis side of the firstsupport portion 74 and a U-form gripper on the y-axis side of thefixation portion. The holding member 77 functions to maintain thedefined relative positions between the substrate 76 and the firstsupport portion 74 constantly by fixing the fixation portion on thefirst support portion 74 while gripping the substrate 76 with thegripper.

The second support portion 72 includes a plate-like body with a circularopening 72 b at the center, a ring-like convexity 72 a on the reversey-axis side of the body to surround the circular opening 72 b, and alens support portion 72 c extending from a lower part of the convexity72 a to the y-axis reverse direction. The lens support portion 72 c hasa groove with a V-form cross section on the top surface along the y axisto retain the coupling element 11 at a predetermined position in the xand z axis directions.

The coupling element 11 has a lens with a refractive index of about 1.5to couple light beams from the light source 10.

The surface of thus-configured second support portion 72 on the y-axisside is fixed at the end of the reverse y-axis side of the first supportportion 74 by screws or the like, for example.

The optical guide system 20 as shown in FIG. 8 comprises a beam splitter21, a collective lens 22, and a reflective mirror 23 which are containedin the first support portion 74.

The beam splitter 21 is a plate-like member with a rectangular openingat the center and has a reflective surface reflecting light beams fromthe light source 10. The beam splitter 21 is retained to be inclined at45 degrees relative to the y axis, to thereby have pass through theopening a part of a light beam incident from the y-axis side and reflectthe rest of the light beam in the x-axis direction.

The collective lens 22 has a positive power and collects the light beamreflected in the x-axis direction by the beam splitter 21 on the lightreceiving surface of the light receiving element 18 via the reflectivemirror 23.

The light source unit 70 is, for example, configured to be rotatablysupported around the optical axis of the coupling element 11 by fittingthe convexity 72 a of the second support portion 72 into the opening ofa support member 101 of an optical housing or the like, as shown in FIG.9. Accordingly, rotating the light source unit 70 relative to theoptical elements after the aperture member 201 makes it possible toadjust the light beams to be collected on the photoconductive drums witha predetermined pitch in the sub scan direction. Also, the light sourceunit 70 is configured to be supplied with electric power from anexternal power supply via the connector 80 which is provided near thex-axis end of the y-axis side surface of the substrate 76.

Referring back to FIG. 2, the aperture member 201 has a rectangularopening whose longitudinal direction is the x-axis (main scan) directionand is disposed so that the center of the opening is positioned at oraround the focus position of the coupling element 11 (FIG. 4) of thelight source unit 70, for example.

The beam splitter prism 202 vertically (sub scan direction) splits alight beam having passed through the opening 21 a of the beam splitter21 into two light beams separated with a predetermined distance.

The liquid crystal elements 203A, 203B are vertically adjacent to eachother to correspond with the two split light beams and deflect the lightbeams in the sub scan direction according to a voltage signal suppliedfrom a not-shown controller.

The cylindrical lenses 204A, 204B are vertically adjacent to each otherto correspond with the two split light beams and collect the incidentlight beams on the polygon mirror 104. The cylindrical lenses 204A, 204Bhave positive curvature at least in the sub scan direction, and functiontogether with later-described toroidal lenses 107A to 107D as an opticalface tangle error correction system which make deflection points on thedeflection surface of the polygon mirror 104 conjugated with thephotoconductive drums 30A to 30D in the sub scan direction.

The polygon mirror 104 is a pair of square prism members havingdeflection surfaces on side faces, and the two members are verticallyadjacent to each other and shifted in phase from each other at 45degrees. It is rotated at a certain angular velocity by a not-shownrotary mechanism in a direction of arrows in FIG. 2. The light beams arevertically split into two by the beam splitter prism 202 of the opticalincidence system 200A or 200B and collected and deflected on the upperand lower deflection surfaces of the polygon mirror 104 respectively,thereby making the light beams incident alternatively on thephotoconductive drums.

The fθ lenses 105, 305 each have image height in proportion with theincidence angle of the light beam and move, at a constant velocityrelative to the Y-axis, an image plane of the light beam deflected atthe certain angular velocity by the polygon mirror 104.

The reflective mirrors 106A, 106B, 306C, 306D are placed so that theirlongitudinal direction is to be the Y-axis direction, to return thelight beams having passed through the fθ lenses 106, 305 to be incidenton the toroidal lenses 107A, 107B, 307C, 307D.

The toroidal lenses 107A, 107B, 307C, 307D are placed so that theirlongitudinal direction is to be the Y-axis direction, to focus thereturned light beams on the surfaces of photoconductive drums 30A to 30Dvia the reflective mirrors 108A, 108B, 308C, 308D whose longitudinaldirection is the Y-axis direction, respectively.

Optical detectors 141A, 141B are placed near the ends of the beamincidence surfaces (Y-axis side) of the toroidal lenses 107A, 107B whileoptical detectors 141C, 141D are placed near the ends of the beamincidence surfaces (reverse Y-axis side) of the toroidal lenses 307C,307D. Similarly, optical detectors 142A, 142B are placed near the endsof the reverse Y-axis side of the toroidal lenses 107A, 107B whileoptical detectors 142C, 142D are placed near the ends of the Y-axis sideof the toroidal lens 307C, 307D. The optical detectors 141A to 141D,142A to 142D output signals which turn on only while the light beam isincident.

Next, operation of the image formation apparatus 500 incorporating theoptical scan apparatus 100 will be described. Upon receiving imageinformation from a higher-level device or the like, a light beam fromthe light source unit 70 of the optical incidence system 200A passesthrough the aperture member 201 to be adjusted in beam form and is splitvertically into two. The split light beams transmit through the liquidcrystal elements 203A, 203B, respectively to be therebyposition-corrected in the sub scan direction, and then are collected onthe deflection surface of the polygon mirror 104 via the cylindricallenses 204A, 204B. The light beams deflected by the polygon mirror 104are incident on the fθ lens 105.

The upper light beam incident on the fθ lens 105 is reflected by thereflective mirror 106B and incident on the toroidal lens 107B. Thetoroidal lens 107B collects the light beam on the surface of thephotoconductive drum 30B via the reflective mirror 108B. Meanwhile, thelower light beam incident on the fθ lens 105 is reflected by thereflective mirror 106A and incident on the toroidal lens 107A. Thetoroidal lens 107A collects the light beam on the surface of thephotoconductive drum 30A via the reflective mirror 108A. With the phaseshift at 45 degrees between the upper and lower deflection surfaces asdescribed above, the photoconductive drums 30B, 30A are alternativelyscanned with the upper and lower light beams in the reverse Y axisdirection according to the output signals from the optical detectors141A, 141B, 142A, 142B, respectively.

Similarly, a light beam from the light source unit 70 of the opticalincidence system 200B passes through the aperture member 201 to beadjusted in beam form and is split vertically into two. The split lightbeams transmit through the liquid crystal elements 203A, 203B,respectively to be thereby position-corrected in the sub scan direction,and then are collected on the deflection surface of the polygon mirror104 via the cylindrical lenses 204A, 204B. The light beams deflected bythe polygon mirror 104 are incident on the fθ lens 305.

The upper light beam incident on the fθ lens 305 is reflected by thereflective mirror 306C and incident on the toroidal lens 307C. Thetoroidal lens 307C collects the light beam on the surface of thephotoconductive drum 30C via the reflective mirror 308C. Meanwhile, thelower light beam incident on the fθ lens 305 is reflected by thereflective mirror 306D and incident on the toroidal lens 307D. Thetoroidal lens 307D collects the light beam on the surface of thephotoconductive drum 30D via the reflective mirror 308D. With the phaseshift at 45 degrees between the upper and lower deflection surfaces asdescribed above, the photoconductive drums 30C, 30D are alternativelyscanned with the upper and lower light beams in the Y axis directionaccording to the output signals from the optical detectors 141C, 141C,142D, 142D, respectively.

Further, in the light source unit 70 a light beam from the light source10 is reflected by the reflective surface of the beam splitter 21 andincident on the light receiving element 18 via the collective lens 22and the reflective mirror 23. In the light source unit 70 signals areoutputted when the light beam is incident on the light receiving element18 and they are constantly monitored to adjust amount of the light beamfrom the light source 10.

Specifically, after deflected by the polygon mirror 104 but beforereaching the scan area of the photoconductive drum, the light beam isreceived by the light receiving element 18 which outputs a photoelectricconversion signal upon receipt. The light source unit 70 is configuredto detect intensity of the light beam from the light source 10 accordingto the photoelectric conversion signal from the light receiving element18 and set a value of a current supplied to each VCSEL so that theintensity of the light beam is to be a preset value. Accordingly, havingpassed through the opening 21 a of the beam splitter 21, the light beamat the preset intensity is incident on the scan areas of thephotoconductive drums 30A to 30D. The value of current is reset uponcompletion of scanning the scan areas and set again before the nextscanning. Thus, output of each VCSEL is adjusted for every scanning.

The photoconductive layers on the surfaces of the photoconductive drum30A, 30B, 30C, 30D are charged with the electric chargers 32A, 32B, 32C,32D at a predetermined voltage, therefore, electric charges aredistributed at a fixed density thereon. When the photoconductive drums30A, 30B, 30C, 30D are scanned with the light beams, portions of thephotoconductive layers on which the light beams are gathered becomeconductive and the electric potential of the portions is substantiallyzero. Accordingly, by scanning the photoconductive drums 30A, 30B, 30C,30D rotating in the direction indicated by the arrows in FIG. 1 with thelight beams modulated according to the image information, electrostaticlatent images defined by distributed charges are formed thereon.

The develop rollers of the toner cartridges 33A, 33B, 33C, 33D in FIG. 1supply toners to the electrostatic latent images on the surfaces of thephotoconductive drums 30A, 30B, 30C, 30D, respectively. At this point,since the develop rollers of the toner cartridges 33A, 33B, 33C, 33D(develop unit) are charged with a voltage of reverse polarity of that ofthe photoconductive drum 30A, 30B, 30C, 30D, the toners attached to thedevelop rollers are charged with the same polarity of that of thephotoconductive drum 30A, 30B, 30C, 30D. Because of this, the toners arenot attached to the portions on which the electric charges aredistributed but only attached to the portions scanned with the lightbeams. Thereby, the electrostatic latent images are visualized as tonerimages on the surfaces of the photoconductive drum 30A, 30B, 30C, 30D.

As described above, the respective toner images formed by the first tofourth image formation stations according to image information aresuperimposedly transferred onto the surface of the transfer belt 40. Thetoner images on the transfer belt 40 are transferred by the transfercharger 48 onto the paper sheets 61 extracted from the paper feed tray60 and fused by the fuse roller 50. The paper sheets 61 with the imagesthereon are discharged by the discharge roller 58 and stacked upsequentially in the paper discharge tray 501 a.

As described above, the light source unit 70 according to the presentembodiment comprises the bias member 78 which biases the substrate 76towards the first support portion 74 so that the surface of the lightsource 10, specifically, the surface (reverse y-axis side) of thepackage 10 b (FIG. 7(A)) is brought in contact with the bottom wall ofthe concavity 74 b by pressure. This enables precise positioning of thelight source 10 relative to the first support portion 74. Further, afterthe bias member 78 defines the positional relation between the substrate76 and the first support portion 74, the holding member 77 is fixed tothe first support portion 74 while the gripper is gripping the substrate76. Thereby, it is possible to constantly maintain the defined relativepositions between the substrate 76 and the first support portion 74,resulting in constantly maintaining the positional relation between thecoupling element 11 supported by the second support portion and thelight source 10.

Moreover, the holding member 77 as shown in FIG. 8 grips theneighborhood of the connector 80 on the substrate 76. This can preventthe relative position between the substrate 76 and the first supportportion 74 from being changed due to receiving the impact fromattachment/detachment of the wiring from/to the connector 80, or thesubstrate 76's accidentally getting in contact with other componentsduring maintenance work or the like, for example.

The bias member 78 is configured to have the anchor portions 78 b to beinserted through the slits 76 b on the substrate 76, when fixed to thefirst support portion 74. This also makes it possible to prevent therelative position between the substrate 76 and the first support portion74 from being changed.

Further, the optical scan apparatus 100 according to the presentembodiment comprises the light source unit 70 in which the holdingmember 77 can stably maintain the positional relation between the lightsource 10 and the coupling element 11. This can avoid varying theimaging characteristics of the light beams on the photoconductive drums30A to 30D over time, enabling stable, accurate scanning on thephotoconductive drums 30A to 30D.

Further, the light source unit 70 is rotatably disposed around theoptical axis of the coupling element 11. Accordingly, rotating the lightsource unit 70 relative to the optical elements after the aperturemember 201 makes it possible to adjust the light beams to be collectedon the photoconductive drums with a predetermined pitch in the sub scandirection.

Further, the image formation apparatus 500 according to the presentembodiment forms images based on the electrostatic latent images formedby the optical scan apparatus 100. Therefore, it can stably formaccurate images on the paper sheets 61.

Moreover, in the image formation apparatus 500 according to the presentembodiment, the beam splitter 21 is configured to split the light beamsfrom each VCSEL of the light source 10 by having only the light beamincluding chief ray pass therethrough and reflecting the other lightbeams. This makes it possible to scan the photoconductive drums 30A to30D with the light beams with high intensity having passed through theopening 21 a, and at the same time use the light beams not contributingto scanning for the intensity monitoring. In this manner, light beam useefficiency can be improved.

Second Embodiment

Next, the second embodiment of the present invention will be describedwith reference to FIGS. 10 to 14. A description on the same componentsas those in the first embodiment will be simplified or omitted

FIG. 10 shows a light source unit 70′ according to the secondembodiment. The light source unit 70′ is different from the light sourceunit 70 in that the substrate 76 and the first support portion 74 arejoined by use of a pair of holding members 81, 82.

FIG. 11A perspectively shows the holding member 81 while FIG. 11Bpartially shows a side thereof. The holding member 81 is formed by pressworking or sheet metal processing on a metal plate. The holding member81 is composed of three parts, a rectangular fixation portion 81 a whichis long in the z-axis direction, a plate-like latch portion 81 c with aV-form notch (engaging portion) 81 d from an upper end to the center, aconnection portion 81 b to connect the fixation portion 81 a and thelatch portion 81 c when they are in parallel to each other, as shown inFIG. 11A. The fixation portion 81 a has long holes 81 e adjacent witheach other and long in the z-axis direction. As shown in the explodedview in FIG. 11B, the notch 81 d of the latch portion 81 c is formed insuch a shape that the two side lines get narrower in width in the y-axisdirection as they go downwards (reverse z-axis direction). The width ofthe bottom thereof is set to be equal to or smaller than the thicknessof the substrate 76.

Similarly, FIG. 12A perspectively shows the holding member 82 while FIG.12B partially shows a side thereof. The holding member 82 is formed bypress working or sheet metal processing on a metal plate. The holdingmember 82 is composed of three parts, a fixation portion 82 a which islong in the y-axis direction, a plate-like latch portion 82 c with anotch (engaging portion) 82 d from an upper end to the center, aconnection portion 82 b to connect the fixation portion 82 a and thelatch portion 82 c when they are in parallel to each other, as shown inFIG. 12A. The fixation portion 82 a has long holes 82 e adjacent witheach other in the y-axis direction and long in the z-axis direction. Asshown in the exploded view in FIG. 12B, the notch 82 d of the latchportion 82 c is formed in such a shape that the two side lines getnarrower in width in the y-axis direction as they go downwards (reversez-axis direction). The width of the bottom thereof is equal to orsmaller than the thickness of the substrate 76.

Referring to FIGS. 10, 13, such a holding member 81 is fixed on the sidesurface (x-axis side) of the first support portion 74 with bolts 85 viathe long holes 81 e of the fixation portion 81 a, with the latch portion81 c projected from the x-axis side of the first support portion 74.Likewise, the holding member 82 is fixed on the side surface (reversex-axis side) of the first support portion 74 with not-shown bolts 85 viathe long holes 82 e of the fixation portion 82 a, with the latch portion82 c projected from the y-axis side of the first support portion 74. Theholding members 81, 82 are configured to be vertically movable by thebolts 85's sliding in the long holes 81 e, 82 e, respectively.

As shown in FIG. 13, the substrate 76 includes, at upper end of thereverse x-axis side and lower end of the x-axis side, holes 76 c, 76 dwhich are long in the z-axis direction. The first support portion 74 andthe substrate 76 are fixed by fitting the light source 10 and the lightreceiving element 18 into the concavities 74 b, 74 c of the firstsupport portion 74 (FIG. 6) and then joining the first support portion74 and the substrate 76 with the latch portions 81 c, 82 c of theholding members 81, 82 inserted through the holes 76 c, 76 d,respectively.

Then, by moving the holding members 81, 82 upwards relative to thesubstrate 76 and the first support portion 74, as shown in FIGS. 11B,12B, the notches 81 d, 82 d of the holding members 81, 82 are engagedwith the holes 76 c, 76 d while the bottom portions of the holdingmembers are in contact with the substrate 76. The holding members 81, 82are firmly fixed to the first support portion 74 by fastening the bolts85 fitted into the first support portion 74. In this manner thesubstrate 76 can be fixed on the first support portion 74 at the definedposition in the y-axis direction.

Moreover, the light source unit 70′ includes a connector 80 on thereverse y-axis side surface of the substrate 76, as shown in FIGS. 13,14 for example. The connector is placed on a straight line on the hole76 d and in parallel to the z axis, to be connected with an externalwiring 80 a (FIG. 14) from below.

As described above, the light source unit 70′ according to the presentembodiment is configured to include the holding members 81, 82 so thatthe first support portion 74 and the substrate 76 can be fixed at thedefined relative position by fixing the fixation portions 81 a, 82 a onthe first support portion 74 while the notches 81 d, 82 d are engagedwith the substrate 76. This allows the relative position between thefirst support portion 74 and the substrate 76 to be constantlymaintained, resulting in constantly maintaining the relative positionbetween the coupling element 11 on the second support portion 72 and thelight source 10.

Further, disposing the connector 80 on the straight line on the hole 76d and in parallel with the z axis can effectively reduce a displacementin the positions of the substrate 76 and the first support portion 74due to external force from connecting/disconnecting (putting in/pullingout) the external wiring 80 a to/from the connector 80. In general,detachment of the external wiring 80 a is likely to be done carelessly.Aiming for preventing this from happening, the holding members 81, 82according to the present embodiment are configured to support thesubstrate 76 from below by the notches 81 d, 82 d.

In the present embodiment, the notches 81 d, 82 d are formed in such ashape that the two side lines get narrower in width in the y-axisdirection as they go downwards (reverse z-axis direction). The width ofthe bottom thereof is set to be equal to or smaller than the thicknessof the substrate 76. This can especially achieve more precisepositioning of the substrate 76 in the y-axis direction. However,without assembling easiness taken into consideration, the notch 81 d canbe shaped such that the width of the two side lines in the y-axisdirection is equal to the thickness of the substrate 76 at any point.Further, the width thereof in the y-axis direction need not be equal toor smaller than the thickness of the substrate in order to avoid thepositional shift of the first support portion 74 and the substrate 76due to external force from the z-axis direction alone.

When the external wiring is attached/detached to/from the connector 80on the substrate 76 in the y-axis direction, the connector 80 ispreferably disposed close to the holding members. For theattachment/detachment in the other directions, optimally adjusting theposition and direction of the holding members makes it possible toconstantly maintain the relative position of the first support portion74 and the substrate 76.

According to the present embodiment, the respective portions of theholding members 81, 82 are shaped with precision by press working orsheet metal processing. Accordingly, the engaging portions can beengaged with the substrate 76 firmly.

The present embodiment has described an example where the notches 81 d,82 d of the holding members 81, 82 are engaged with the holes 76 c, 76d. However, the present invention is not limited thereto. The holdingmembers 81, 82 can be configured to be engaged with the outer edgeportion of the substrate 76, or notches formed on the outer edgeportion.

Also, the present embodiment has described an example where the relativeposition of the first support portion 74 and the substrate 76 are fixedby the two holding members 81, 82. However, the number of holdingmembers can be three or more, or only one, for example, the holdingmember 82 only. In this case, it is also possible to reduce momentaround the y axis on the substrate 76 due to the external force from thedetachment/attachment of the external wiring 80 a from/to the connector80.

In the first embodiment, the holding members are placed at the fixedpositions on the first support portion 74 while in the secondembodiment, they are movable in the z-axis direction. Alternatively, theholding members may be movable in the y-axis direction relative to thefirst support portion 74.

In such a case, as shown in a light source unit 70″ in FIG. 15, thefirst support portion 74 and the substrate 76 are joined with each otherwhile a pair of holding members 77 are fitted into two outer ends of thesubstrate 76. Then, in FIG. 16, by relatively moving the holding membersto the first support portion 74 in the reverse y-axis direction, thesubstrate 76 is bent to generate elastic force on the light source 10 inthe reverse y-axis direction. This can firmly bring the reverse y-axisside surface of the light source 10 in contact with the bottom wall ofthe concavity 74 b on the first support portion 74 by pressure.

The first and second embodiments have described the multi-color imageformation apparatus 500 with the plurality of photoconductive drums 30Ato 30D. However, the present invention is not limited thereto. Thepresent invention is applicable to a mono-color image formationapparatus which scans a single photoconductive drum with a plurality oflight beams.

Further, the first and second embodiments have described an examplewhere the optical scan apparatus 100 is applied to a printer. However,the present invention is not limited thereto. The optical scan apparatus100 is suitable for other image formation apparatuses besides a printer,such as a photocopier, a facsimile machine, or the combination of suchdevices.

As exemplified above, the light source unit according to the presentinvention is configured to accurately position the light source relativeto the first support portion. Also, after the relative position isdefined by the bias member, the substrate and the first support portionare fixed by the holding member. Accordingly, the relative positionbetween the substrate and the first support portion can be constantlymaintained, so that consequently, the positional relation between thecoupling element supported by the second support portion and the lightsource can be constantly maintained.

Further, the light source unit according to the present invention isconfigured to include the bias member with the anchor portion.Therefore, it is possible to prevent a change in the relative positionbetween the bias member and the substrate.

Further, the light source unit according to the present invention isconfigured to include the holding member movable in the optical axis ofthe coupling element. Accordingly, by bowing the substrate, elasticforce to the coupling element acts on the light source. Thereby, it ismade possible to firmly bring the surface of the light source on thecoupling element side into the bottom wall of the concavity by pressure.

Further, according to the present invention, it is possible to prevent achange in the relative position between the substrate and the firstsupport portion when attaching/detaching the wiring to/from theconnector or when in handling the light source for maintenance purpose,the substrate is accidentally made in contact with another component,for example.

Further, the optical scan apparatus according to the present inventionis configured to include the above-described light source unit so thatit can scan the scan surfaces of the photoconductive drums stably andaccurately without variation in the imaging characteristics of the lightbeams over time.

Further, in the optical scan apparatus according to the presentinvention, the light source unit is configured to be rotatably supportedaround the optical axis. Therefore, rotating the light source unitrelative to the optical elements after the aperture member makes itpossible to adjust the light beams to be focused on the photoconductivedrums with a predetermined pitch in the sub scan direction.

Further, the image formation apparatus according to the presentinvention is configured to include the above-described optical scanapparatus so that it can form accurate images on the recording mediumstably.

Although the present invention has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations may be made in the embodiments described by persons skilledin the art without departing from the scope of the present invention asdefined by the following claims.

1. A light source unit comprising: a light source with a plurality oflight emission portions two-dimensionally arranged; a substrate on whichthe light source is mounted; a first support portion supporting thesubstrate; a bias member biasing the substrate towards the first supportportion; a coupling element coupling a light beam emitted from the lightsource; a second support portion supporting the coupling element; and aholding member holding a position of the substrate relative to the firstsupport portion.
 2. A light source unit according to claim 1, wherein:the light source comprises a light emitting element including aplurality of light emission portions and a package containing the lightemitting element; and in order to position the light source relative tothe first support portion, the bias member biases the substrate towardsthe first support portion to make the package in contact with the firstsupport portion.
 3. A light source unit according to claim 1, whereinthe bias member comprises an anchor portion which latches the substrateto restrict movement thereof in a direction orthogonal to an opticalaxis of the light source.
 4. A light source unit according to claim 1,wherein the holding member is attached to the first support portion andis movable in an optical axis direction of the coupling element.
 5. Alight source unit according to claim 1, wherein the holding member isattached to the first support portion and comprises an engaging portionwhich is engaged with the substrate.
 6. A light source unit according toclaim 5, wherein the holding member holds the substrate in a directionorthogonal to an optical axis of the coupling element.
 7. A light sourceunit according to claim 6, wherein the engaging portion is formed in oneof wedge and trapezoid shapes.
 8. A light source unit according to claim1, comprising a plurality of holding members holding a position of thesubstrate relative to the first support portion.
 9. A light source unitaccording to claim 1, further comprising a connector mounted on thesubstrate and connected with a wiring from outside, wherein the holdingmember holds neighborhood of a portion of the substrate on which theconnector is mounted.
 10. A light source unit according to claim 9,wherein the holding member is disposed on a line in parallel to adirection from which the connector is connected or disconnected with thewiring.
 11. An optical scan apparatus scanning a scan surface with alight beam, comprising: a light source unit according to claim 1; anoptical deflector deflecting a light beam emitted from the light sourceunit; an optical imaging system focusing the light beam deflected by theoptical deflector on the scan surface.
 12. An optical scan apparatusaccording to claim 11, wherein the light source unit is rotatablysupported around the optical axis of the coupling element.
 13. An imageformation apparatus which forms a toner image according to anelectrostatic latent image obtained by image information, and fuses thetoner image on a recording medium for image formation, comprising: anoptical scan apparatus according to claim 12; a photoconductive drum onwhich an electronic latent image is formed by the optical scanapparatus; a develop unit visualizing the electrostatic latent imageformed on the photoconductive drum; and a transfer unit fusing a tonerimage visualized by the develop unit on a recording medium.